1. Field of the Invention
The invention relates to an apparatus for mounting and unmounting a tire on a rim, having a device for firmly holding the rim, a motor for rotating the rim, a device for pulling the bead edges of the tire over the wheel flange, and a device for forcing the bead edges of the tire into the rim bed.
2. The Prior Art
A tire mounting apparatus is known in which a rim is firmly gripped with clamping claws on the table of a clamping fixture. The rim is rotated via an electric motor, which is provided with a transmission, so that a tire mounting tool introduced between the wheel flange and the bead of the tire pulls the tire off the rim or pulls it onto the rim, as applicable. The bed of the rim is used for this process. Three or four self-centering clamping claws of the clamping fixture lock the rim from the inside on the rim key, or from the outside on the wheel flange. The clamping fixture must assure that the rim is centered exactly so that the tire mounting tool always remains spaced apart from the wheel flange during the rotation of the rim. The clamping claws are controlled via pneumatic cylinders.
The first step in removing a tire is to force the beads of the tire into the bed of the rim, from their seat on the wheel flange, by means of a forcing tool. As a rule this tool is mounted on the side of the apparatus and is actuated via a pneumatic piston/cylinder unit. To force a tire off a rim, the forcing tool must be used at several points on both sides of the tire, and after being forced off on one side the tire has to be turned over. The forcing tool in the known apparatus requires considerable force, which is exerted on the side of the tire and is difficult to control.
Damage to the tire and rim cannot be precluded in that case. Especially with wide tires, it can often happen that in the process of forcing the tire off the rim the forcing tool can be forced into the bed of the rim, and can damage the rim bed.
The known tire mounting apparatus requires a great number for providing units of force, such as an electric motor and pneumatic piston/cylinder units. Also, a transmission between the electric motor and the rotating plate of the clamping fixture is indispensable. Furthermore, the known apparatus is complicated to use and is not always problem-free.